An Interdisciplinary Framework for Sustainable Tart Cherry (Prunus cerasus L.) Production

Farmer’s Agroecological Knowledge

The results of grower interviews yielded several interesting trends that reveal grower agroecological knowledge and their diverse strategies for overcoming numerous constraints. These trends help explain why growers use sustainable practices and/or strive for sustainability. While there are many different orchard management strategies, in general, specific management strategies tend to be related to farm scale. As consolidation has occurred in the tart cherry industry, three size classes of tart cherry farms have emerged. Because of consistently low cherry prices over the last twenty years, scale-related management strategies are near fully driven by the need to cut production costs. Large-scale operations

The largest farms generally use some form of integrated pest management (IPM), scout for pests, use degree day models to predict the timing of pest and disease pressure, closely monitor weather conditions, and spray alternate rows. Increasing production efficiency is often paramount for these growers and several have built custom equipment to do so. For instance, one fairly large grower suggested,

“We are even trying to cut more trips [through the orchard] out. I need to get a mower company to make me a 13 ft. mower to tow behind the sprayer. I think they will build me one this winter. The orchard will look like hell because only ½ the orchard will get mowed every two weeks, but you’ve got to cut costs. If we were making money it might not be as important to think about making fewer trips through the orchard.” Leelanau County grower

Other large growers have built their own thousand gallon spray trucks, which are faster than conventional spray rigs, are more mobile, and make it easier to access distant orchards. For these growers attempting to maximize efficiency, ¾ mile long rows and 250 acre blocks are not uncommon.

“Ten years ago I had six full-time employees, now I have three. We are always trying to cut costs, and that’s why we own air curtain sprayers. People thought we were crazy-$50,000 a piece, but I cut chemical costs 30-40%. It doesn’t take long to pay for them. We were trying to replace a piece of equipment every other year so nothing in our operation was over eight years old. We had to put that on hold.” Leelanau County grower

Disease problems are typically managed by several applications of broad-spectrum fungicides. Arthropod pests are typically managed by several applications of broad-spectrum organophosphate insecticides, which are intended to kill the pests before they can physically damage the fruit. At a bare minimum, conventional growers will apply a ½ side (every other row) of organophosphate early in the season for plum curculio and another ½ side later for cherry fruit fly. One large grower, who has cut rates substantially over the last dozen years, still uses at least five fungicide applications. Growers must also think about and contend with orchard re-entry times after applying pesticides. By law after applying azinphos-methyl (Guthion), the most commonly used insecticide, growers must wait two weeks before re-entering the orchard. Thus growers must weigh whether to spray two weeks before harvest with an effective insecticide or push the envelope and apply a less-effective insecticide with a shorter re-entry time closer to harvest.

Nearly all tart cherry growers apply some form of nitrogen fertilizer to tart cherry trees. Liquid or granular, fertigated, banded or broadcast, on average growers apply 90-100lbs actual N/acre (Nugent pers comm. 2005). In 2003, 92% of Michigan tart cherry acres received N application, while 64% received potash (K) and 33% received phosphate (USDA NASS 2004b). In the 1960’s most growers switched from clean cultivation to seeded sod alleys and herbicide tree rows to control erosion and maintain long-term orchard productivity. This practice is still typical today; herbicides are applied to 65% of tart cherry acreage. To reduce tree injury caused by mechanical harvesting and facilitate the harvest process, a single application of Ethephon, a fruit loosener, is typically applied 1-2 weeks prior to harvest. Gibberellic acid is used to increase spur numbers thereby promoting increased fruit capacity and long-term productivity. In 2003 Ethephon and Gibberellic acid were applied to 80 and 33 percent of MI tart cherry acreage respectively (USDA NASS 2004c).

Medium-scale operations

Most conventional small and medium sized farms use very similar pest, disease, and fertility management strategies but are constrained and save funds by diligently maintaining old equipment. One grower suggested “you could easily spend $500,000 on new equipment, a new shaker alone is $160,000, but we don’t generate that kind of revenue.” Another says:

“I have been very fortunate to get people on in my situation just big enough to offer a fair amount of money to my crew so they can come and work and do their hours… I've been fortunate. I could switch to a harvester and have fewer people, easier, quicker, and probably a better score, better returns. The whole thing would be better. It's just a big commitment. We are working our way towards one. Really I should be looking at a harvester and a different spray delivery system. Those are the areas I need to go. If tart cherries can do it now you know, if we are in a new era where it's profitable most years, I will be able to do that.” Leelanau County grower

Although there are exceptions, within the group of medium sized farms is where pesticides are more likely to be sprayed on a set schedule, independent of weather conditions, or disease and pest pressures. There are a host of reasons for the constraints on mid-sized farms, but the major constraints are time-related. Time is a constraint because many farmers with mid-sized farms support the farm through off-farm income. Also, just as Lighthall (1995) found with Iowa corn and soybean growers, the specific biology of P. cerasus provides growers with only a relatively short temporal window to assure tree productivity and product quality. For instance, mid-sized tart cherry growers cannot afford to wait until the last minute to spray because they have too much acreage to cover, and also they generally cannot afford the expensive, efficient equipment. As one grower suggested, “you can’t always afford to wait, because you can’t always fix it after the fact. If you see rain coming you need to get something on, but this is probably a function of my size. If I had 40 acres I could do it.” Another contends, “During bloom we would put on a protectant spray because we can’t get around to spray everything quick enough after an infection, so we have to do some anticipation.” There are exceptions to the rule however. Another medium sized farmer who worked as an IPM technician at one point in time, cuts costs by intensively scouting and waiting until he knows he has a problem before spraying.

“I always keep it coming at just the right intervals so that I’m not over spraying, but I’m protecting the trees. That way I can save some money, I can save some chemicals, and still get the job done. Some years you save a little bit, some years you may actually use a little more chemicals… typically we save. It’s a money saving, chemical saving program.” Leelanau County grower

The same grower though hasn’t had the funds to upgrade equipment and would like to purchase a new sprayer and shaker for environmental reasons- to reduce pesticide drift and costs.

Small-scale operations

Despite the obvious natural constraints to producing tart cherries, a few relatively small-scale growers are producing organic tart cherries for a variety of reasons (discussed later). These growers need to apply more pesticides more often. One organic grower exclaims “People say ‘so now you don’t have to spray’, but we spray twice as much.” Thus, they are typically limited in the scale they can attain with current technology. For example, one grower suggests:

“And (in terms of organic) you're also looking at a lot smaller number of acres. If you take one farm of significant size and say O.K. go organic. Well how many spray rigs will it's take to do it?” The largest operation in Leelanau has three guys in truck sprayers and a real wizard running their operation. He is coordinating those sprays and helping out himself and they are getting targeted chemical out there in the nick of time, spray after spray and just pedal to the metal three truck sprayers just zooming. Now if you go tell that operation to go organic, and you're talking big old engine drive sprayers and how many of them going everyday? You're not talking just pounds of chemicals, you are talking semi-loads.” Leelanau County grower

Another organic grower suggests: “If we had 20 more acres [they currently have 30] that would probably be all we could handle with the equipment and system we have. That would be a whole change if we went above that-hired help, new machinery.” And another contends that a full industry switch to organic is not likely. “Organic is not really feasible here with fruit. Other crops are more adaptable to that, like beans, or corn, but there are too many diseases and pests with fruit, especially if you are large-scale.”

Despite being small scale, these producers tend to grow a more diversified range of crops over the course of the season and though they have to contend with similar pest and disease pressures they use different techniques. As one grower lamented, “the word control is gone in organic, we have management, or deterrents, but no control”. Another suggests “the whole thing is a learning experience, there is no magic bullet.” In general, organic growers apply more pesticides than their conventional counterparts and to every row, as opposed to alternate row applications. For pest management, they typically use “SurroundWP™”, a kaolin clay based compound that completely coats the leaves and fruit, leaving a protective powder that agitates insects, or “diatomaceous earth”, a silica-based powder that causes insects to dehydrate. Diseases are generally managed by multiple applications of copper and sulfur. Interestingly, growers in the past used these same methods for disease control. As one organic grower noted, “that’s how they did it 30-40 years ago, so that’s what I did. I went and talked with the old-timers and my dad…you have to be an agricultural archeologist”. The same grower also contends that there are differences between conventional and organic. “We could wait until the computer told us to spray with the conventional IPM system. But with organics you are back to a protectant program. You have to have the leaves covered before the rain to prevent disease. Basically it’s sulfur and copper.” Fertility management differs between organic and conventional and among organic growers themselves. Organic growers use composted chicken and dairy manure, feathermeal, molasses, seaweed, and even hay grown with septage.

While cherries have been produced in Michigan for over a century, using continuously improving production methods, not least mechanized harvesters, tart cherry growers are still plagued by numerous constraints that threaten their continuance. Though many of these constraints are typical of farming operations across the U.S., several are unique to tart cherry production in northern Michigan. These constraints are shaped by both the socio-natural conditions of tart cherry production and the neoliberalized political economy of Michigan’s tart cherry industry.

Farmer’s Coping Strategies
Large-scale

Growers with large operations in particular see increases in efficiency and production through economies of scale as inevitable, and the only way to remain viable in the industry.

“The switch from handpicking to mechanical harvesting is around 100:1 ratio in terms of productivity. We are fortunate to have a commodity that has leant itself to mechanization. If we didn’t have that productivity increase we would be competing with low wage Chinese labor.” Antrim County grower

Large-scale growers tend to be vertically integrated-they generally do their own processing, and develop and market their own products. They save money by purchasing or even building the latest, most efficient equipment, thereby reducing the costs associated with managing large farm operations (eg. frequent pesticide applications). Though many large scale growers feel they are merely undertaking the logical steps they need to remain economically viable, several growers also expressed concern at the broader increasing trend toward large corporate farms:

“When I was a kid there were a lot of 100 acre farms. They’re all gone now. In twenty years it will either be big 2000 acre farms or people with 20-40 acres working in Traverse as their day job and farming as a hobby. A guy with 100-150 acres can’t survive today. In the County here there will probably be four of us in twenty years growing 70% of the fruit. The small mom and pops will be gone and that is sad. It will be corporate farming.” Leelanau County grower

“As a society, we don't get to see farms now. They're very large farms, but we are losing touch with reality. I think everyone should smell the smell of chickens, pigs, cows and horses, and they should be able to drive down the road and know the difference. People drive down the road and say oh there's manure. I'll drive down the road and say oh cows, pigs, chickens. I know the difference because I grew up with it and I had a chance to smell the difference and I think everybody should have the opportunity to walk into their local slaughterhouse. I mean, they ought to be able to take their pigs over here and watch them be slaughtered. Or have the ability to do that. To be so isolated from the process. You are liable to say, the factory farms we should not have those anymore. Maybe we should have all the farming happened in Bolivia, why not have South America supply us with these animals. There are supplying us with cherries now and oranges. Why not animals? It's something we don't need to have in this country. I think we're getting so far from reality. From what I understand the animals, cattle, mainstream commercial cattle in Michigan are trucked out of the state to be slaughtered and then the meat is trucked back in. It just seems so odd to me. I don't even know what to say about it.” Leelanau County grower

Small and medium scale

The medium and small sized growers have typically foregone purchasing new equipment by diligently maintaining older equipment, and in effect have relied on their own labor and off-farm income to remain in farming. When I asked growers if they had used off-farm income to sustain their orchard, one grower replied without hesitation, “How do you think we survived?” Other northern Michigan cherry growers expressed similar sentiments:

“Well they [bad years] cause me to look off the farm for work. If we were to sell the farms right now, we would be fine. We are both working off the farm. That's kind of what it has forced me into, is to go off the farm. The farm has become evenings and weekends for me. It is still a significant part of my income per se, but I have not been able to buy a harvester, which is something that I really should do. I will get a new harvester and gradually step away from my off farm work and become just a farmer and we will be doing well. We are at a position where we could do that. Tart cherries are going to have to do it though. In my mind, if we're going to have any significant farms in the county it's the cherry industry; it has to be surrounding tart cherries. The apple deal is gone pretty much. We are not processing apples really, there is no money there. Some guys are doing fresh apples. The guys that are doing grapes more power to them, and we can do quite a few. But that is not going to provide farms for the county-we’ll have grape patches. As you can see we have a significant amount of wineries without a huge number of acres. We will be able to do a certain amount and those guys come in typically pretty well funded. If you do that though you have to be able to put it into a bottle and sell it. As a niche market this area has developed a name and you can sell a $10 or $12 bottle of wine or $15 to $28 bottle of champagne, and that's pretty upscale. And people are spending it because it is unique and cool and we’re not going to compete on the volume. We’re going to compete on a niche market. That will be there and there are some other little patches that will be there, but the farms will have to be tart cherries.” Leelanau County grower

“If you went back to the 40s we were making a better living in the 40s than we actually are now-more disposable income in the 40s and early 50s because living costs weren’t as high and you could buy a tractor for 5000 dollars. Now that same tractor is 35 or 40 thousand dollars. So yes we are actually living on less than we had back then. Of course we have more things, but if it weren’t for an outside income other than farming we wouldn’t be here now.” Leelanau County grower

Small and medium scale growers, encouraged by potential price premiums, have sought to expand into the organic market in an attempt to regain control of the marketing of their product. They have diversified into other products as well. All of the growers I interviewed who have organic acreage have done so for economic reasons. When asked what changes would be necessary to make a decent living farming?, one organic grower responded: “That’s why we have gone organic-the changes aren’t out there, so organic might be a window.” For another organic grower, the switch to organic wasn’t a big leap but was also based upon the dire economic situation in the cherry industry: “organic was just an extension of what we were already doing. In our organic applications, the goal was to have sustainable self sufficiency-both. As self sufficient as you can be…cut out the marketers and suppliers and take your share back. That is what is driving some of our ideas.” A third organic grower agreed: “we always tried to be sustainable, so the transition to organic was easy to make. The main motivation is economic.” When asked what changes they would make if cherries were more profitable, one grower’s response was indicative of grower’s reasons for adopting certified organic practices on their farms-to regain some control over the production and marketing of their tart cherries:

“It’s not if cherries are more profitable, it’s when tart cherries are more profitable. Because one thing that we have learned-if we don’t get our price the fruit doesn’t leave the farm. I am not selling at a loss just to keep the damn system going. If we are not happy with the price, then they sit right here. So you are taking back some control and hopefully some money but the risk isn't any less. It can’t be because the risk for total failure is greater….and we will work with someone on a payment schedule. It’s not like we have to be paid on the day of harvest or one week after harvest…We can work together with them [processors]. We are not separate from them. We have got to work together as a team. Before, as conventional farmers, all you do is harvest your crop and give it to the processors and you walk away. There is no connection there-either we are the bad guys or they are the bad guys, and they just sell them to Sara Lee or wherever else and have no hand in it. There has to be some sort of team.” Benzie County grower

Besides advocating new marketing partnerships, the organic growers I interviewed also enjoyed the inherent challenge of organic production. “Because it is more fun, more challenging, and because there is more thinking involved” were three reasons growers gave for transitioning. Organic growers also highlight intangible benefits as well:

“Well we weren't happy farming the other way, we weren't having fun at all. I’ve only got one chance at this and I'm only going through this life once, and by God it’s not going to be without having some fun. Organic is fun in general. It benefits your mind about fifty years right from the start. As far as practices, and products that you can use, there is a whole lot of stuff…it’s communication too, you have to talk to other farmers, you have to be around people. Even if you are not talking about the same thing, there is an energy that’s there that you take with you. If they are talking about raising strawberries and we are talking cherries, it really doesn’t matter. It’s a struggle for a common goal-how to achieve it. You need to have that kind of shared…“the agony of defeat”, you need to have that, and we discovered that. Fifty years ago there was a farming community. You were at each others house on Sunday and there were organizations and impromptu groups. You paid your bills in person and after harvest that was a big deal for the next two days. It was a sense of community, there was a connection there and that needs to be part of it.” Benzie County grower

In terms of organic certification, most of the organic growers I interviewed have chosen to have their crops certified by the Organic Crop Improvement Association International (OCIA) rather than Organic Growers of Michigan (OGM). However, certification with OCIA is more stringent because they demand a plan from each grower that demonstrates their willingness to transition their entire farm to organic within five years. But because it is internationally recognized, certification with OCIA provides guaranteed access to global markets. Producing high-quality certified organic cherries that can be sold in the markets with the most stringent organic standards provides growers with a sense of pride as the following quotation notes:

“We could have gone with Organic growers of Michigan (OGM), but I don’t know where my marketing is going to take me. It was one of those intuition things that said go for the big boys and cover your bases. And when it comes to selling my product, whether it will be in raw form or processed form, we don’t know. I want to be able to say with confidence, just like we have always done conventionally, that we raise the best product that we can. Our quality is excellent. We were always in the top 10% of the processing plant grade. And we strive for that and we will achieve that by God. And if you are going to have anything it’s going to be a quality product. There is a market for black and white brand generic and Spartan brand and everything else, but that is not where I am heading. It’s a fine market but I am heading for the food buyer, the top. Because that is where I want our product to be.” Benzie County grower

All of the organic growers that I interviewed displayed a cautious optimism about the future. “There should be money enough on a relatively small acreage to at least make 20-30 thousand a year and still work for 6 months out if you wanted to. There ought to be that.” Despite their optimism, they all expressed doubts about the future of the organic industry in general. The prevailing reason for this attitude was the thought that the organic industry would most likely be taken over by large corporations if it becomes feasible on a large scale. One organic grower lamented “the big chains will most likely take organic over and drive the price down.” Another expressed concern that in the future only corporate farms with ample resources will be able to afford expensive pest and disease control products:

“Now the government is getting into organics and it has already had a big effect changing the certification process and what that means. The National Organic Label may be usurped by the big growers because they have the resources to deal with all of the regulations. It looks like they are taking out some of the stuff [organic certified chemicals] we were using. The marketers and suppliers and big guys are getting into organics and making [pest and disease control] products that are really expensive and the big growers can afford it. The whole thing will be usurped I am afraid. In the future, the mechanism will be the big grower whereas before organic was the niche of the small grower.” Leelanau County grower

Groundcover Management Systems

Leaf Nutrients and Yield

After three years of treatments, there were no significant differences in leaf nitrogen (%) (Control= 2.23+/-.06 s.e., Five Species Mix= 2.25 +/- .07 s.e., Clovers/Mustard= 2.16 +/- .04 s.e., Rye/Vetch= 2.12 +/- .03 s.e.) or other leaf nutrient levels between treatments and the conventional system. While weed biomass or the limited amount of side-delivered mulch may have partially sustained tree nutrient levels, we did not directly measure groundcover nutrient levels. Growers may need to apply compost or mulch to sustain tree leaf nutrient levels in the long-term.

Initial tree circumference averaged 64 cm +/- 1.38 (s.e.), and did not vary significantly among treatments and the conventional sod treatment. Baseline yields of tart cherries in 2000 averaged 5653 kg/ha +/- 437.5 (s.e.), and in 2001 averaged ca. 2.5x greater than the initial year (p<.001). There were no significant yield (kg/ha) differences among the three alternative groundcover treatments and the conventional sod treatment however (Control= 13738 +/- 809 s.e., Five Species Mix= 14490 +/- 1368 s.e., Clovers/Mustard= 14127 +/- 1018 s.e., Rye/Vetch= 17129 +/- 995 s.e.). There were also no differences in yield (kg/ha) between mulched and conventionally managed plots in 2001 (mulched 14562+/-665 s.e., conventional managed 15227+/-892 s.e.). In 2002 there were not enough cherry yields to justify harvesting; we only collected one year of post-baseline yield data and relied upon grower estimates in the following years. While this limits our ability to draw solid conclusions, our data suggest that there was no evidence of yield reduction due to ½ rate fertilizer or herbicide elimination in the alternative GMS treatment plots. In 2003 the grower removed a block of trees for replanting that included one of our treatment replicates. In both 2003 and 2004, the farmer reported that treatment trees remaining yielded above average compared to other tart cherry blocks owned by the grower (R. Fouch, pers. comm. 2004). In a long-term experiment, Landis et al. (2002) demonstrated that alternative orchard floor and nitrogen management in Michigan did not reduce tart cherry yield. Swezey et al. (1998) also reported that no yield declines were associated with increased weed biomass in an organic system after three years of transition from conventional to organic apple production. There are several potential explanations for our results. First, the treatment trees were nearing twenty-five years old, presumably have well-established, relatively deep root structures, and perhaps exploit a different resource niche (in space or time) than understory vegetation (Hall 1995). While yields were not reduced for these older, well-established trees, understory vegetation has been shown to compete for nutrients with newly planted tart cherry trees (Anderson et al. 1992) and peach trees (Belding et al. 2004) that extract nutrients and water from similar soil zones. Second, the timing of weed control may also play a role in maintaining tree vigor and productivity. In apple orchards, the potential for weed competition declines through the growing season and with tree age (Merwin and Ray 1997). Merwin and Stiles (1994) noted no significant differences in apple tree growth or yield when comparing year round herbicide-maintained bare ground tree rows and post-emergent Roundup treatments that resulted in substantial weed growth by early fall. Third, conventional management may be inefficient in terms of nutrient cycling (N overuse, inefficient application, or inefficient uptake by tart cherry trees). After three years of alternative management, the results of our tree leaf nutrient analyses suggested no evidence of alley cover crops or tree row weeds competing with trees for nitrogen, although yields were very low for much of this period. Weinbaum (1992) contends that in orchards, nitrogen use efficiency (NUE) is generally less than 25%. Several researchers have found high rates of nitrate leaching in orchards. Merwin et al. (1996) noted greater sub-surface nitrate concentrations in conventional, pre-emergent and post-emergent herbicide managed apple orchards. Edson et al. (2003) reported roughly nine times greater quantities of Nitrate N (lb/A/yr) leached in conventional cherry orchards when compared to alternative GMSs. In Michigan, the majority of tart cherry production occurs on sloping sites with sandy soils prone to leaching (Cavigelli 1998). Tree row vegetation may reduce leaching by scavenging excess nutrients and releasing them upon decay in the spring, thereby improving soil quality and providing nutrients to the crop tree. Reducing fertilizer rates and/or improving the timing of fertilization can increase tree NUE and also reduce leaching potential. For example, Linhard and Hansen (1997) demonstrated that cherry flowers per bud, fruit set, and yield were lower when nitrogen was applied late in the previous growing season. They suggest that growers should consider only adding N fertilizer in the spring and early summer. Fertigation, the injection of N into trickle irrigation, 3-4 times per year may also be a more efficient alternative to a single broadcast N application (Hanson and Proebsting 1996) and when combined with cover crops, has been shown to decrease leaching and increase profitability in tart cherry orchards (Edson et al. 2003). Fourth, in addition to scavenging for excess nutrients, tree row vegetation can act as a winter and spring mulch layer and maintain higher soil moisture levels than bare ground tree rows (Walsh et al. 1996, Longstroth and Perry 1996). Because bare ground soils generally encourage early emergence of weed sprouts (Watt 1970), tree-row vegetation can provide a physical barrier to weed growth in the spring, the time of maximum tree nutrient uptake in orchard systems in the eastern U.S. (Merwin 2003). Groundcover and mulch GMS treatments had an effect on compositional cover, plant species richness, and functional group richness. Cover crops established well in the first year and persisted through at least three seasons without reseeding for the five species mix and clovers/mustard GMSs. However, in the second year, the rye/vetch treatment was out-competed by other vegetation. Proportionally, legume species accounted for the majority of total cover for both the five species mix and clovers/mustard treatments from May 2001-August 2002. Both red clover (T. pratense) and white clover (T. repens) dominated the understory vegetation producing vigorous stands each year. Species composition and percent cover of the conventional sod treatment did not vary noticeably over time and was primarily comprised of quackgrass (E. repens) and roughstalk bluegrass (P. trivialis). Cereal rye (S. cereale) and brown mustard (B. juncea) did not establish well and were both virtually absent by August 2002. Hairy vetch (V. villosa) established well by fall 2000, but declined each subsequent year due to competition from other species (mainly Taraxacum officinale Weber, Common dandelion) or from lack of winter hardiness at 45 N latitude (Teasdale et al. 2004). Also, red and white clover became the dominant species (compositional cover) in both the five species mix and the clovers/mustard GMSs over the course of our experiment. This may explain the overall decrease in plant species richness and plant functional group richness for these two treatments when compared to the conventional system in 2002. Depending upon their specific reasons for planting groundcover, growers should consider the growth habits and competitive status of specific groundcover plant species. While there were significant differences among treatments for all vegetation factors (Compositional cover: p<.001; plant species richness: p<.001; functional group richness: p<.001), there was also a significant interaction between time and treatment in each case. Therefore, we compared treatments for each date separately. The five species mix and clovers/mustard treatments provided more cover than the conventional system on all dates, and in general all three alternative groundcover treatments had significantly higher levels of plant species richness and functional group richness than the conventional system. Not surprisingly, elimination of mid-late summer herbicide treatment led to greater vegetative growth in the tree rows of all three treatments compared to the herbicide treated control (p<.001). However, like alley compositional cover, there was also an interaction between date and treatment. Separate analyses for each date revealed an interesting trend. In Spring 2002 (May), there was significantly more weed growth in the conventional system tree rows than the rye/vetch and five species mix tree rows. For three sample dates there was a significant effect of treatment on percent of vegetation-free area (p<.001). Like the previous examples however, time interacted with treatment. Upon further analyses, both the five species mix and rye/vetch GMS had significantly higher percentages of vegetation free area when compared to the control. The addition of litter to tree rows using side-delivery mulch from the alleys did not reduce weed growth (compositional cover) when compared to the non-mulched plots. There was no significant difference between the mulched and non-mulched sub-treatments in compositional cover. The result of biomass samples suggests there was not enough side-delivery mulch to significantly reduce understory weed growth in the tree rows. Although it had the lowest alley compositional cover, the control yielded the highest mean alley vegetation biomass (1.5Mg/ha dry weight), followed by the clovers/mustard treatment (1.4 Mg/ha dry weight), the mix (1.3 Mg/ha dry weight) and the rye/vetch treatment (1.1 Mg/ha dry weight). Although our results suggest that mowed side-delivered mulch at 1-1.5 Mg/ha/year had negligible effects on weed suppression and yield, in spring 2002 we found greater weed growth in the conventional system tree rows compared to the five species mix, and rye/vetch GMSs. Extensive fall weed biomass in the GMS tree rows created a mulch layer that may have delayed growth of spring weeds. We expect further benefits at higher mulch levels, whether through the application of off-farm mulch or high biomass on farm mulch species. Edson et al. (2003) found that supplemental straw mulch [10Mg/ha per year (dry weight)] significantly reduced weed growth and increased tart cherry yield. Additionally, the potential for long-term soil quality benefits in orchards should be higher in mulch systems through enhancement of soil fertility. Edson et al. (2003) also found cover crops, and/or mulching increased soil organic matter, beneficial microbes, and soil carbon and nitrogen availability to trees. Soils after eight years of bark mulch in apple orchards had lower bulk density, greater soil porosity, and more rapid water infiltration when compared to pre-emergence and post-emergence herbicide application (Oliveira and Merwin 2001). Mulching has also been shown to increase total soil C in cherry orchards, with the highest gains recorded in a natural species vegetation mix (Sanchez et al. 2003). Additionally, Merwin (2003) found that mulching increased soil N and carbon content two times more than pre-emergent herbicide, post-emergent herb, and mowed sod in apple orchards. Arthropod species richness, abundance, and H’ Our results suggest that GMSs had significant positive effects on arthropod species richness (S), abundance (A), and diversity (H’) (S: p<.001; A: p<.001; H’: p<.05). Because there was a significant season effect, we separated the arthropod data into spring (June) and summer (August) for comparison. Species richness, abundance, and diversity all increased as the community developed over time. The GMSs resulted in changes among trophic groups as well. In terms of trophic group richness and H’, in general there were no significant differences between the GMSs and the control in the spring. However, in the summer all three GMSs resulted in significant species richness and H’ increases for all trophic groups except “other species richness” (not shown). The analyses for trophic group abundance however, yielded somewhat different results. In June, ln(herbivore abundance) was higher in all three GMSs when compared to the control, but not in August. On the contrary, ln(predator abundance) was higher in all three GMSs in August but not in June, and parasitoid abundance was not significantly different in either June or August. In spite of intensive organophosphate insecticide application in our research system, we found higher levels of predator abundance, species richness, and diversity (H’), and higher levels of parasitoid species richness, and diversity (H’) in the GMSs. Researchers have demonstrated natural enemy increases with general cover crop use (Bugg and Waddington 1994, Wyss et al 1995) and increasing cover crop diversity in particular (Altieri 1994, Wyss 1996, Letourneau 1997). And in several cases natural enemies have lowered levels of orchard and vineyard insect pests (Altieri and Schmidt 1985, Blommers 1994-review, Jenser 1999, Nicholls et al. 2000), although not always to economically viable levels (Daane et al. 1998). Though there are multiple ecological approaches for pest management in agricultural systems (Shennan et al. 2005), our results have particular relevance for conservation biological control in tart cherry systems. In Michigan tart cherry orchards there are two major insect pests of concern, the plum curculio (Conotrachelus nenupha) and the cherry fruit fly (Rhagoletis cingulata Loew). Both deposit eggs directly in ripening cherries, the plum curculio early in the spring and the cherry fruit fly nearer to harvest in late-July and early-August. Because the increases in natural enemy levels we noted were not apparent until the August sampling dates, any potential for biological control would most likely be limited to the cherry fruit fly. More research is needed to determine which natural enemy species use the cherry fruit fly as a host. Though a majority of Michigan cherry growers use some form of integrated pest management (IPM), 99% of all U.S. tart cherry acreage receives both insecticide and fungicide sprays (USDA 2002). Chemical intensive agricultural systems have been shown to reduce natural enemy diversity (Andersen and Eltun 2000, Epstein et al. 2000, Miliczky et al. 2000, Brown and Schmitt 2001) and carbamate and organophosphate (OP) insecticides are thought to be the most detrimental to natural enemies (Theiling and Croft 1989). While OP pesticides can limit biocontrol opportunities, the potential for full-scale conservation biological control in cherry systems is most severely limited because of the “zero-tolerance” regulation for internal insect larvae, which completely prohibits any larval damage on fruit. Dr. Larry Olsen, co-director of the USDA North Central Region Pest Management Center and IPM program coordinator suggests that the zero tolerance regulation is the biggest hurdle for pesticide reduction in tart cherry agroecosystems (Curtis 1998). Another pesticide-related constraint that growers face is the potential phase-out of certain organophosphate pesticides because of environmental and health concerns. For instance, the U.S. Environmental Protection Agency has proposed phasing out the most commonly used and most effective insecticide, azinphos-methyl (Guthion) for cherry pests by 2010 (U.S. EPA 2006). Thus, further research into GMSs that provide conservation biological control benefits should be investigated to reduce application of chemical pesticides and to take advantage of the potential organic price premiums.
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